Benzene and heterocyclic rings formation in cycloaddition reactions catalyzed by RuCp derivatives: DFT studies

► CpRuCl complexes catalyze cyclotrimerization of alkynes. ► Metallacyclopentatriene form from coupling of two alkynes. ► A bicyclic biscarbene complex controls the stereochemistry of cyclotrimerization. ► The reaction is exergonic and has low activation barriers according to DFT studies.